Fluororubber is excellent in physical properties such as heat resistance, solvent resistance or chemical resistance in comparison with common rubber compositions, and used for making such products, for example, as hoses, tubes, sealants or the like by taking advantage of this excellent physical property. Such fluororubber is obtained in most cases by curing fluorine containing polymers with organic peroxides.
Known generally as fluorine containing polymers curable with organic peroxides are polymers obtained by copolymerizing bromine containing monomers with fluorine containing monomers while introducing the bromine atoms into the main chain of the polymers. Such fluorine containing polymers have usually been cross-linked to have three-dimentional cross-linked structure by allowing the bromine atom introduced into the main chain to radically undergo elimination addition.
For instance, Japanese Patent Publn. No. 1585/1979 discloses fluorine containing polymers obtained by copolymerizing (1) olefin containing less than 3% of bromine with (2) fluorine containing monomers having 2-7 carbon atoms to give copolymers containing at least 0.05% by weight of bromine. Further, Japanese Patent Publn. No. 4115/1978 discloses fluorine containing polymers obtained by copolymerizing (1) less than 3 mol% of 4-bromo-3,3,4,4-tetrafluorobutene-1 or bromotrifluoroethylene with (2) tetrafluoroethylene and perfluoroalkyl perfluorovinyl ether containing C.sub.1 -C.sub.5 alkyl to give copolymers containing at least 0.05% by weight of bromine. Furthermore, Japanese Laid-Open-to-Public Publn. No. 195113/1985 discloses fluorine containing polymers obtained by copolymerizing monomers represented by ROCX.dbd.CYZ (1 or 2 out of X, Y and Z is bromine or iodine and the rest is hydrogen, fluorine or chlorine).
The fluorine containing polymers disclosed in the above-mentioned publications, however, contain bromine atoms active to organic peroxides, said bromine atoms have been introduced into the main chain or very stiff side chains of the polymer. On that account, there was such a problem that no cross-linked fluorine containing polymers found to be satisfactory in physical properties such as compression set, elongation, tensile strength, 100% modulus, etc. are obtained.
In the case of the monomers represented by ROCX.dbd.CYZ as disclosed in Japanese Laid-Open-to Public Publn. No. 195113/1985, moreover, there was also such a problem that a number of process steps are required for preparing such monomers, taking a great deal of time.
U.S. Pat. No. 3,351,619 Specification, on one hand, discloses fluorine containing polymers obtained by polymerizing iodinated fluoroalkyl containing vinyl ethers, and U.S. Pat. No. 3,306,879 Specification discloses fluorine containing polymers obtained by polymerizing 2-bromoethyl vinyl ether or 2-iodoethyl vinyl ether. In these cases, however, there were such problems that fluorine containing polymers which contain iodine atoms are inferior in photostability and that such hydrocarbon vinyl ethers containing no fluorine atoms as bromoethyl vinyl ethers are inferior in heat resistance, copolymerizability, etc.
The present inventors extensively studied with the view of solving such problems mentioned above as associated with the prior art, and have eventually accomplished the present invention on the basic of their finding that fluorine containing polymers having introduced bromine atoms active to organic peroxides into not the main chain or stiff side chaines but into the side chain having pliability are found, when cross-linked with organic peroxides, to have quite excellent characteristics in physical properties such as elongation, tensile strength, compression set, etc.